2D vs 3D - Existence of 2D materials!?

If you get technical, then every object is 3 dimensional, since it is made of 3 dimensional atoms, so graphene is technically 3 dimensional. A true 2 dimensional object has only length and width with no height whatsoever. However, there are theoretical objects that have only two dimensions or less. For example, the theoretical strings that make up the universe are usually one dimensional loops. As a string moves through spacetime, it creates a two dimensional worldsheet. Theoretically, strings, or branes, can have as much as 10 or 11 dimensions. As far as I know, no 2 dimensional objects have been discovered yet. When they say "2D", they usually mean "extremely thin".